Automatic machine dishwashers are widely used to clean soiled dishes, cooking utensils and other containers for serving and preparing food, such as plates, cups, glasses, silverware, pots, pans, etc., generically referred to as "dishes". While the construction and composition of dishes vary widely, most usually have glossy, solid surfaces on which the presence of dried water spots is readily noticeable. These dried water spots are aesthetically unappealing and thus methods and compositions for reducing their number and size are of great concern to the detergent industry as well as to the consumer.
Typical automatic dishwashers operate by subjecting food-soiled dishes and the like to alternating wash and rinse cycles inside a closed washing chamber. Spray nozzles inside the chamber direct powerful streams of hot wash liquor and rinse water onto the soiled dish surfaces. The force exerted by these pressurized water streams removes a considerable amount of food residue. There is, however, a substantial amount of food residue that resists dislodgment by the water jets. It is known that by adding certain additives to an automatic dishwashing detergent composition, and thereby to the wash water, a much greater quantity of food soil can be removed from soiled article surfaces during the washing cycle.
One type of additive that is often added to automatic dishwashing detergent compositions is a detergent builder. Typical detergent builders include complex phosphates, carbonates, sulfates and silicates. Detergent builders compliment the detersive action of surfactants such as by sequestering certain metallic ions which are present in most water sources. Phosphate-based detergent builders reduce hard water film formation caused by the deposition of metallic precipitates. Another additive included in automatic dishwashing compositions are alkalinity builders. Alkalinity builders provide alkaline cleaning power which is particularly important in automatic dishwashing compositions since, by its very nature, automatic dishwashing does not provide the mechanical action of hand dishwashing. Since physical contact with the wash liquor by the consumer does not occur when dishes are cleaned in a machine dishwasher, alkalinity builders are especially suitable for use in automatic dishwashing detergents. Other additives typically found in an automatic dishwashing detergent include bleaches, enzymes, corrosion inhibitors, surfactants, defoamers, polymers and bleach activators.
However, the addition of chemicals to complement the detersive action of the surfactants used in automatic dishwashing detergents has disadvantages. In particular the addition of complex phosphates to the dishwashing detergent formulation results in soft water corrosion of select surfaces in glassware. Therefore, the addition of phosphates to commercial dishwashing compositions, has the tendency to exacerbate the corrosion of commercial glassware. It is also well known that phosphates contribute to the eutrophication of rivers and lakes. It is therefore desirable to provide a dishwashing detergent that does not use phosphates, therefore, preventing the corrosion of glassware and prevent pollution of the environment while still maintaining acceptable cleaning properties.